This application is a 35 USC 371 application of PCT/DE 00/04246 filed on Nov. 29, 2000.
1. Field of the Invention
The invention relates to a method and an apparatus for making through openings in a high-pressure fuel reservoir.
2. Description of the Prior Art
From German Patent Disclosure DE 196 40 480 A1, a high-pressure fuel reservoir for a fuel injection system for internal combustion engines is known which comprises an elongated, tubular jacket body of steel into which a high-pressure fuel pump can be connected. The jacket body has a longitudinally extending continuous recess, open on at least one end, that forms the interior of the high-pressure fuel reservoir. In the fully installed state of the high-pressure fuel reservoir, the at least one open end is closed by the attachment of the high-pressure fuel pump or of a pressure limiting valve, or in some other way. By way of a plurality of connections embodied on the jacket body and high-pressure lines connected to them, the fuel subjected to high pressure that is contained in the high-pressure fuel reservoir is delivered to electrically controlled injection valves, so-called injectors, for injection into the combustion chambers of a self-igniting internal combustion engine. A high-pressure fuel reservoir of this kind is also known as a common rail. The connections of the high-pressure fuel reservoir are embodied in the form of connection stubs, which protrude from the jacket body and are each provided with a through opening embodied as a bore, which opens into the continuous recess of the jacket body. The through openings can also open eccentrically into the continuous recess.
In the conventional production of the through openings with a machining tool, a more or less markedly pronounced burr surrounding the bore is created at the outlet point of the tool in the continuous recess. Because of the high internal pressure in the high-pressure fuel reservoir, which is about 1350 bar, and because of the narrow diameters of the bores, typically 2.4 mm, abrasive particles in the fuel cause wear in the region of the encompassing edge formed by the through opening and the inner wall of the continuous recess. The occurrence of abrasive particles is disadvantageously further reinforced by the burr surrounding the bore, because relatively large particles can become detached there and damage the injection nozzles. Furthermore, the presence of a burr surrounding the bore favors the development of eddies and unfavorable flow properties, which can very adversely affect the service life of the high-pressure fuel reservoir, given the increasing pressure loads on it.
These disadvantages are reliably avoided by the method for making through openings in a high-pressure fuel reservoir according to the invention. Because before the through opening is made, a pressure part is pressed against the inner wall of the jacket body in the region of the expected outlet of the through opening, and with the machine tool, drilling is done through the jacket body some distance into the pressure part, the occurrence of a burr surrounding the bore is advantageously avoided. This method is especially advantageous at places in the high-pressure fuel reservoir where later metal-cutting deburring is not possible.
It is also especially advantageous that because of the creation of the burr-free bores, a subsequent rounding off or chamfering of the edge formed by the bore and the inner wall of the continuous recess is made possible, so that especially evenly rounded-off or chamfered edge structures can be created. In the prior art, because of the development of a burr in the drilling, these methods do not lead to the desired results.
Advantageously, to produce a through opening, a chucking device that can be introduced into the continuous recess can be used, having a first chucking jaw, an interchangeable pressure part, a second chucking jaw, and a chucking part disposed between the first chucking jaw and the second chucking jaw, by which chucking part the pressure part and the second chucking jaw can be pressed into contact with the inner wall of the continuous recess. Once the bore has been made, which ends in the pressure part in a blind bore, the chucking device is removed from the high-pressure fuel reservoir, and the pressure part is replaced. The chucking device is now ready for use again. Advantageously, the pressure part can be used as an insertion part inserted into a recess of the first chucking jaw. The pressure part comprises metal or a very hard plastic, which is approximately equivalent in its hardness to the hardness of the jacket body.
Advantageously, the radius of curvature of the face of the pressure part oriented toward the inner wall of the continuous recess is adapted precisely, at the point intended for making the through opening, to the radius of curvature of the inner wall of the continuous recess.
An apparatus for rounding off the encompassing edge formed by the through opening and the inner wall of the continuous recess, which includes both a laser beam shining axially into the applicable bore and displaceable perpendicular to the axis of the bore and a rotating deflection mirror inclined relative to the laser beam, which mirror is mounted on a slide that is provided with an annular gear and can be introduced into the continuous recess, is also advantageous.
For chamfering the encompassing edge formed by the through opening and the inner wall of the continuous recess, a grinding device with a conical grinding head that can be introduced into the continuous recess is also advantageous. Advantageously, the grinding device is disposed on a rod. The motion of the grinding head in the continuous recess is controllable in such a way, by a drive unit acting on the rod, that the grinding head is moved along the edge contour in accordance with a preset program. Dimensional tolerances in the edge contour can be compensated for by a spring bearing of the grinding head.